The present invention relates to well logging and, in particular, to a means for displaying the data obtained from a well logging tool that cyclicly scans the wall of the borehole such as described in U.S. Pat. No. 3,369,626. This type of logging tool referred to as a borehole televiewer or BHTV, emits a pulse of acoustic energy directed at the borehole wall and records the reflected signal. In addition, the tool provides a pulse indicating when the acoustic pulse was initiated and a synchronizing pulse which indicates a geographical direction in each scan of the tool, normally North.
Various types of display systems have been devised for displaying characteristics of the reflected signal which in turn relate to the condition of the borehole wall. For example, in the patent referred to above, the signals are used to control the brightness or Z axis of the oscilloscope trace while the horizontal or X axis sweep is controlled by the sync signal. Thus, a new sweep of the oscilloscope is initiated for each complete scan of the borehole. By photographing the face of the oscilloscope, one obtains a record of the condition of the borehole from which one can locate fractures and similar characteristics.
In U.S. Pat. No. 3,668,619 there is disclosed an improved display system which utilizes an oscilloscope and displays each scan of the borehole as a loop-shaped trace, preferably in an eliptical form. By displaying the traces in this form, one obtains a record which has the appearance of a borehole. The patent also describes systems by which various portions of the eliptical trace may be intensified to illustrate different sections of the borehole wall.
While both of the above display systems provide useful information relating to the condition of a borehole wall, they have several disadvantages. For example, it is impossible to process the data to remove unwanted signals or to emphasize particular characteristics. Further, the only method for obtaining a permanent record is to photograph the face of the oscilloscope. This, of course, eliminates the possibility of re-displaying the data on the oscilloscope face when the operator desires to recheck a portion of the borehole. At times it may be desirable to re-play a portion of the data so that the logging tool can be re-run in certain sections of the borehole prior to leaving a well site.